I know something similar has been asked before but it was different as in just wanting to know what happens to the fuel of a fire and I didn’t exactly find the information I’m looking for.
My question is, I guess, more so asking for specific details about combustion.
Google’s online dictionary basically explained combustion as the process of fire “consuming” it’s fuel.
I was then wondering if this was comparable, even if only in analogy, to fire actually eating the fuel like maybe the matter which said fuel is composed of actually transforms Into fire as it burns rather than only producing fire as it breaks down from burning.
In: Chemistry
Chemical bonds break with enough heat and oxygen. The fuel breaks into other things, and the fire is the energy released in the breakage. That energy pushes nearby fuel to its breaking point, and the cycle continues as long as there is fuel, oxygen, and heat remaining. The temperature when the fuel ignites depends on the material.
The fuel, consisting of hydrogen and carbon (a hydrocarbon such as petroleum or wood), combines with with oxygen from the atmosphere to form carbon dioxide (CO2) and water vapor (H2O). The chemical reaction gives off heat and light.
Fire is a chemical reaction between some flammable material and oxygen. A lot of our fuels (gasoline, natural gas etc) are hydrocarbons, consisting simply of carbon and hydrogen. In an idealized situation called complete combustion, these would react with oxygen to form carbon dioxide and water vapor.
For instance the complete combustion of methane, the main component of natural gas is:
CH₄ + 2O₂ —> CO₂ + 2H₂O
Realistically, you usually get some products of incomplete combustion such as carbon monoxide and soot.
Combustion proceeds by breaking apart the fuel molecules and reacting them with oxygen molecules, producing water and carbon dioxide (unless there’s no carbon in the fuel), in addition to other products depending on what the fuel actually is. As each fuel molecule breaks apart, the chemical bonds release their stored energy as heat, which helps overcome the ignition energy of neighboring fuel molecules, and continues the reaction.
Everything continues until you run out of oxygen, fuel, or energy to sustain the reaction.
The actual flame is composed of larger fuel molecules that don’t end up fully reacting with oxygen, and are just superheated to the point that they glow in the (typically) visible spectrum. Other parts of the flame are particles within the fuel (e.g. soil) that can’t burn, but which can still decompose under high heat and be converted into gas, which *also* tend to glow. The flame is a consequence of combustion, although the flame does represent areas of relatively high heat, meaning areas where combustion can spread easily if there is available fuel and oxygen.
Fire isn’t really a “thing”, it’s a process.
When the fuel ignites, it starts a chemical reaction. The molecules in the fuel and in the air rearrange themselves into new molecules (aka smoke, ash, and gasses like water vapor and carbon dioxide).
The reaction also releases a bunch of energy. All that energy heats up the molecules involved in the reaction. Hot enough that they visibly glow. It’s exactly the same as a really hot chunk of metal. It’s just the particles are so small that they can be suspended and float in the air.
In other words, fire is just smoke that’s still red hot.
The fuel oxidises and produces heat. The flames you see are usually the products of this oxidation.
Ethanol for example is C2H6O. When it burns it combines with O2 in the atmosphere and makes CO2 and H2O and a lot of heat.
The flames you see are carbon dioxide and water vapor heated up so much that they emit light.
Fire is considered a plasma. It is a substance in a transitory state. So yes, the fuel, and air are very briefly fire as they break down into their combustion products.
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